st: xttobit and u normally distributed

I would like to learn how to check the assumption in the Random Effects Tobit model that the unit-specific residuals (u) are normally distributed. Predicting u is not an option after xttobit, as can be done after xtreg. How do I assess the fit of my xttobit model to see whether I may interpret it's results?
I am using intercooled Stata 7.
I am looking forward to an answer!
Greetings,
M. (Marieke) Verschuuren, MD
Junior researcher MTA
Julius Centre
UMC Utrecht
The Netherlands
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